AN/FLR-9

The AN/FLR-9 is a type of very large circular "Wullenweber" antenna array, built at eight locations during the cold war for HF/DFdirection finding of high priority targets. The worldwide network, known collectively as "Iron Horse", could locate HF communications almost anywhere on the planet. Because of the exceptionally large size of its outer reflecting screen (1056 vertical steel wires supported by 96 120-foot towers), the FLR-9 was commonly referred to by the nickname "Elephant Cage." Constructed in the early to mid 1960s, in May 2016 the last operational FLR-9 at Elmendorf-Richardson in Alaska was decommissioned.[1] It can be confused with the US Navy's AN/FRD-10, which also used a Wullenweber antenna.

Advances in technology have made the FLR-9 obsolete. In 1997, the FLR-9 at the former Clark AB in the Philippines was converted into a 35,000-seat fabric-covered amphitheatre. In early May 2002, systematic dismantling of the FLR-9 at San Vito began, and it was totally deconstructed by the end of that month. Although the markings of where the array stood remain in the ground, the structure is completely gone.[5]